On Wed, Jul 22, 2020 at 2:31 AM 'Fangrui Song' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote: > > When CROSS_COMPILE is set (e.g. aarch64-linux-gnu-), if > $(CROSS_COMPILE)elfedit is found at /usr/bin/aarch64-linux-gnu-elfedit, > GCC_TOOLCHAIN_DIR will be set to /usr/bin/. --prefix= will be set to > /usr/bin/ and Clang as of 11 will search for both > $(prefix)aarch64-linux-gnu-$needle and $(prefix)$needle. > > GCC searchs for $(prefix)aarch64-linux-gnu/$version/$needle, > $(prefix)aarch64-linux-gnu/$needle and $(prefix)$needle. In practice, > $(prefix)aarch64-linux-gnu/$needle rarely contains executables. > > To better model how GCC's -B/--prefix takes in effect in practice, newer > Clang (since > https://github.com/llvm/llvm-project/commit/3452a0d8c17f7166f479706b293caf6ac76ffd90) > only searches for $(prefix)$needle. Currently it will find /usr/bin/as > instead of /usr/bin/aarch64-linux-gnu-as. > > Set --prefix= to $(GCC_TOOLCHAIN_DIR)$(CROSS_COMPILE) > (/usr/bin/aarch64-linux-gnu-) so that newer Clang can find the > appropriate cross compiling GNU as (when -no-integrated-as is in > effect). > > Cc: stable@xxxxxxxxxxxxxxx > Reported-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx> > Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > Tested-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Link: https://github.com/ClangBuiltLinux/linux/issues/1099 > --- > Changes in v2: > * Updated description to add tags and the llvm-project commit link. > * Fixed a typo. > > Changes in v3: > * Add Cc: stable@xxxxxxxxxxxxxxx > --- > Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/Makefile b/Makefile > index 0b5f8538bde5..3ac83e375b61 100644 > --- a/Makefile > +++ b/Makefile > @@ -567,7 +567,7 @@ ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),) > ifneq ($(CROSS_COMPILE),) > CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%)) > GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit)) > -CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR) > +CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(CROSS_COMPILE) CROSS_COMPILE may contain the directory path to the cross toolchains. For example, I use aarch64-linux-gnu-* installed in /home/masahiro/tools/aarch64-linaro-7.5/bin Basically, there are two ways to use it. [1] PATH=$PATH:/home/masahiro/tools/aarch64-linaro-7.5/bin CROSS_COMPILE=aarch64-linux-gnu- [2] Without setting PATH, CROSS_COMPILE=~/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu- I usually do [2] (and so does intel's 0day bot). This patch works for the use-case [1] but if I do [2], --prefix is set to a strange path: --prefix=/home/masahiro/tools/aarch64-linaro-7.5/bin//home/masahiro/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu- Interestingly, the build is still successful. Presumably Clang searches for more paths when $(prefix)$needle is not found ? I applied your patch and added -v option to see which assembler was internally invoked: "/home/masahiro/tools/aarch64-linaro-7.5/lib/gcc/aarch64-linux-gnu/7.5.0/../../../../aarch64-linux-gnu/bin/as" -EL -I ./arch/arm64/include -I ./arch/arm64/include/generated -I ./include -I ./arch/arm64/include/uapi -I ./arch/arm64/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi -o kernel/smp.o /tmp/smp-2ec2c7.s Ok, it looks like Clang found an alternative path to the correct 'as'. But, to keep the original behavior for both [1] and [2], how about this? CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE)) Then, I can get this: "/home/masahiro/tools/aarch64-linaro-7.5/bin/aarch64-linux-gnu-as" -EL -I ./arch/arm64/include -I ./arch/arm64/include/generated -I ./include -I ./arch/arm64/include/uapi -I ./arch/arm64/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi -o kernel/smp.o /tmp/smp-16d76f.s > GCC_TOOLCHAIN := $(realpath $(GCC_TOOLCHAIN_DIR)/..) > endif > ifneq ($(GCC_TOOLCHAIN),) > -- > 2.28.0.rc0.105.gf9edc3c819-goog > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200721173125.1273884-1-maskray%40google.com. -- Best Regards Masahiro Yamada
